(1) Field of the Invention
The present invention relates to a lens driving devise used in an optical recording/reproducing apparatus for a recording medium such as a compact disc (CD) and a DVD, and an optical pickup equipped with such a lens driving device.
(2) Prior Art
In recent years, optical recording/reproducing apparatuses for compact mass recording media, such as CDs and DVDs, have become widely used for recording pictures, sounds, and other information.
An optical recording/reproducing apparatus reads information by irradiating the recording surface of a recording medium such as an optical disc with a laser beam using a lens and observing the light reflected from the recording surface. The information is recorded along a spiral track on the recording surface.
Here, when the recording medium distorts or deforms, or when a turntable on which the recording medium is mounted tilts or precesses, the distance between the recording surface and the lens changes and the laser beam fails to focus on the recording surface. Also, when the recording medium or the turntable is decentered, the track is displaced in the direction of the radius of the medium and departs from an optical path of the laser beam.
In order to prevent read errors caused by these factors, the lens is moved up and down in the direction of its optical axis (hereafter called xe2x80x9cfocusing directionxe2x80x9d) to focus the laser beam on the recording surface. Also, the lens is moved in the direction of the radius of the medium (hereafter called xe2x80x9ctracking directionxe2x80x9d) to position the optical path of the laser beam on the track.
To move the lens in such ways, the lens is usually mounted on a movable member, and a driving unit moves the movable member to adjust the focal point and the optical path of the laser beam. Also, the recording medium is rotated at high speed (200-500 rpm in a CD, 1,000 rpm or higher in a DVD) in the optical recording/reproducing apparatus, so that the lens has to be quickly moved to the target position. However, natural oscillations of the lens driving device or the optical pickup itself cause instability in the control system.
To suppress the oscillations, Japanese Laid-Open Patent Application No. H7-105551 discloses a lens driving device in which a movable member including a lens is held like a cantilever by a fixed member via a linear elastic supporting member, and a viscoelastic damping member is positioned on the side of the fixed member surrounding the root of the elastic supporting member. With this construction, the oscillations of the elastic supporting member are absorbed by the damping member, and as a result, the oscillations of the lens are suppressed.
However, the damping member in the lens driving device described above is not effective enough to suppress the substantial oscillations of the elastic supporting member, due to the following reason. In the oscillations which have the length of the supporting member as a fundamental wavelength, higher order components are lower in amplitude than lower order components, so that the higher order components are difficult for the damping member to absorb.
Also, because of the construction of the lens driving device in which the movable member including the lens is held like a cantilever by the fixed part via the elastic supporting member, the size of the lens driving device tends to be large in the longitudinal direction of the elastic supporting member.
The first object of the present invention is to provide a lens driving device constructed rationally for an optical recording/reproducing apparatus. The second object of the present invention is to provide a lens driving device that effectively suppresses higher order oscillations. The third object of the present invention is to provide a lens driving device that is compact enough to be used for a reproducing apparatus for recording media such as DVDs. These objects are achieved by a lens driving device that consists of a lens, a base, a damping member that is made of a material which is viscoelastic and holds the lens in the state of being movable in relation to the base, and a driving means for driving the lens in a given direction.
A material which is viscoelastic can suppress oscillations through its vibration absorbency. When a lens is held by a supporting member made of such a material, oscillations of the lens are suppressed regardless of the direction of the oscillations, and the size of the lens driving device become smaller.
In addition, the second object of the present invention is to provide an optical pickup equipped with the lens driving device descried above. The object can be achieved by an optical pickup that consists of a semiconductor laser component, a lens for condensing a laser beam emitted from the semiconductor laser component on a recording surface of an optical recording medium, photoreceptors that receive a returning laser beam from the optical recording medium, an enclosure that holds the lens and contains the semiconductor laser component and photoreceptors arranged in a state of having a predetermined positional relationship, a base, a damping member that is made of a material which is viscoelastic in any direction and holds the enclosure in the state of being movable in relation to the base, and a driving means for driving the enclosure in a given direction.